USB worms have taken the No. 1 spot for top malware in the world, according to a McAfee threat report, released Tuesday. In addition, the “McAfee Threats Report, First Quarter 2010” indicated a trend of diploma spam coming from China and other Asian countries, while spammers are continuing to exploit high-profile news events, such as the Haiti earthquake, by poisoning search engines. Finally, the report found that U.S.-based servers continue to host the majority of malicious URLs.